The HuffPo article mentions that the measure actually requires a _plan_ rather than _action_:
Quote
HuffPo
The proposal, sponsored by Sierra Club spinoff Restore Hetch Hetchy, would require San Francisco to prepare a plan to transition away from one of its primary water sources, the Hetch Hetchy Reservoir in Yosemite National Park.
But doesn't point out what I had heard on a KCBS "in depth" on this issue (while driving towards Yosemite...) - the plan would then face a second public vote.
Which I think is fine, and in fact I think it exposes opponents of the measure. If I lived in SF I'd wonder why opponents don't even want the question investigated with no commitment for action, why do they fear simple investigation of alternatives unless they think some might exist? After all, opponents aren't arguing against planning with no expectation of action (a reasonable thing to argue against), they seem to be claiming that the mere act of planning is a threat.